Method for improving motion times of a stage

ABSTRACT

Methods and systems for, in one embodiment, accelerating a stage through a clearance height in a first direction and decelerating the stage in the first direction while accelerating in a second direction are shown. The stage is moved in a third direction and a determination is made whether the stage movement in the second direction is below a threshold value before continuing to move the stage further in the third direction. The first direction is perpendicular to the second direction and is parallel and opposite to the third direction.

RELATED APPLICATIONS

This is a continuation of application Ser. No. 12/334,378, filed on Dec.12, 2008 now U.S. Pat. No. 8,120,304, entitled “Method For ImprovingMotion Times Of A Stage”, and is related to U.S. patent application Ser.No. 11/335,081 entitled “Methods and Apparatuses for ImprovedStabilization in a Probing System” by Nayak et al., filed on Jan. 18,2006, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to systems and methods for improving the motiontimes of a stage during probing, inspection, assembly, or manufacturingof a component.

BACKGROUND OF THE INVENTION

Probing involves contacting a pad surface of an integrated circuit witha probe tip. The process involves positioning of probe pads relative toprobe tips. The positioning of probe pads, in one system, is achieved bymoving the wafer containing the devices under test. From a set of padsunder test to the next set of pads, the motion consists of moving thepads away from the pins, moving the wafer such that the next set of padsare under the probe tips, and moving the pads toward the probe tips tomake contact with the probe tips.

Since extreme precision is involved in positioning the pads under thepins, it is necessary to control the mechanical motion of the waferprecisely. Any unwanted motion in cross directions can damage the deviceunder test. Consequently, extreme care is taken to ensure thatmechanical motions are well controlled before making contact with theprobe tips.

FIG. 1 a shows a common stage motion profile 20 where a stage moves froma contact position 22 to a clearance height position 24 by single axismotion (often in a vertical or “Z” direction). The clearance height isdefined as the height at which the stage can be moved safely withoutdamaging system components. The stage then moves to another commandedstage position 26, equal to the height of the clearance height,whereafter the stage moves to another contact position 28. The entiremotion profile 20 is shown by three line segments 30, 32, 34.

FIG. 1 b shows an acceleration profile superimposed on the segments 30,32, 34. The first acceleration profile has two segments 36, 38 that canbe viewed with reference to the acceleration axis a1 and distance axisd1. The second acceleration profile having two segments 40, 42 can beviewed with reference to the acceleration axis a2 and distance axis d2.The third acceleration profile having two segments 44, 46 can be viewedwith reference to the acceleration axis a3 and distance axis d3. Thesegments 36, 38, 40, 42, 44, and 46 do not represent a direction ofmovement; rather, they show periods of acceleration or deceleration.

The first acceleration profile shows an acceleration 36 to a midpoint 48being equidistant between the contact position 22 and clearance heightposition 24. After reaching the midpoint 48 distance, the stagedecelerates during the second segment 38 until the stage reaches astopping point at the clearance height 24. It will be understood thatthe only motion which occurs in the first acceleration profile is avertical motion which includes both a period of acceleration (segment36) and a period of deceleration (segment 38). The second accelerationprofile shows an acceleration 40 and a deceleration 42 with a midpoint50. It will be understood that the only motion which occurs in thesecond acceleration profile is a horizontal motion which includes both aperiod of acceleration (segment 40) and a period of deceleration(segment 42). The third acceleration profile has an acceleration 44 anda deceleration 46 to arrive at another contact position 28. It will beunderstood that the only motion which occurs in the third accelerationprofile is a vertical motion which includes both a period ofacceleration (segment 44) and a period of deceleration (segment 46).

Therefore, in the Z-direction, half of the movement in the Z-directionis spent accelerating while the other half of the movement in theZ-direction is spent decelerating.

The single axis motion described requires a verification that motion iscomplete and disturbances are minimized before moving the wafer in thenext axis. This is necessary for both wafer and probe card safety.

SUMMARY OF THE DESCRIPTION

Improved methods and systems are provided for increasing the efficiencyof a stage motion between two positions. The stage may hold a deviceunder testing or inspection or in a manufacturing process or may holdprobe tips or other testing or inspection components. The testing orinspection may be performed vertically or horizontally.

According to one embodiment of an aspect of the invention, a stage isaccelerated through a clearance height in a first direction. After theaccelerating through the clearance height, the stage is decelerated inthe first direction while accelerating the stage in a second direction.The stage is then moved in a third direction.

A determination may be made as to whether the movement in the seconddirection of the stage is below a threshold value before continuing tomove the stage further in the third direction. The first direction isperpendicular to the second direction and parallel and opposite to thethird direction.

According to yet another embodiment of another aspect of the invention,a method of moving a stage in a first vertical direction beyond aclearance height is described. The stage continues to move in the firstvertical direction and begins to move in a lateral direction. The stageis then moved in a second vertical direction to a settle check point.

According to yet another embodiment of another aspect of the invention,a stage is accelerated in a vertical direction through a clearanceheight during a first time period and decelerated during a second timeperiod. The first time period is greater than the second time period.

According to yet another embodiment of another aspect of the invention,a machine readable medium having stored thereon data representingsequences of instructions, which when executed by a computer systemcause the computer system to perform a method of moving a stage isdescribed.

According to yet another embodiment of another aspect of the invention,a base and stage supported by the base are described. The stage isconfigured to move in a three-dimensional coordinate system. At leastone motor is connected with the stage for moving the stage in thethree-dimensional coordinate system. The motor is configured toaccelerate the stage through a clearance height in a first direction andthe at least one motor is configured to decelerate the stage in thefirst direction and to accelerate the stage in a second directionsimultaneously with decelerating the stage in the first direction. Atleast one sensor is coupled with the stage and the sensor is configuredto measure a stage parameter. A control system is coupled with the atleast one sensor. The control system is configured to receiveinformation from the at least one sensor and determines operationparameters of the motor based on a clearance height parameter.

According to yet another embodiment of another aspect of the invention,a support frame and base supported by the support frame is described. Astage supported by the base that is configured to move in athree-dimensional coordinate system having three axis of motion is alsodescribed. At least one motor is connected with the stage for moving thestage in the three-dimensional coordinate system. The motor isconfigured to accelerate the stage through a clearance height in a firstaxis of motion and decelerate the stage in both the first axis of motionand second axis of motion simultaneously. At least one sensor is coupledwith the stage and the sensor is configured to measure a stageacceleration.

The solutions provided by at least certain embodiments of the inventionthus results in a system that improves the stage motion time betweencontact or testing or inspection or manufacturing positions. These andother embodiments, features, aspects, and advantages of the presentinvention will be apparent from the accompanying drawings and from thedetailed description and appended claims which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings in which likereferences indicate similar elements and in which:

FIG. 1 a shows a side view of a prior art motion profile of a stage.

FIG. 1 b shows a side view of a prior art acceleration profile of astage.

FIG. 2 illustrates a side view of a possible embodiment of a probertesting system and its two main stages.

FIG. 3 illustrates a top view of a prober system.

FIG. 4 illustrates a side view of a stage contact position between probepins and conductive elements, according to one possible embodiment.

FIG. 5 a illustrates a side view of a stage motion profile, according toone embodiment.

FIG. 5 b illustrates a side view of a stage acceleration profile,according to one embodiment.

FIG. 6 a illustrates a side view of a stage in a horizontal probingoperation, according to another embodiment.

FIG. 6 b illustrates another side view of a stage in a horizontalprobing operation, according to another embodiment.

FIG. 6 c illustrates another side view of a stage in a horizontalprobing operation, according to another embodiment.

FIG. 6 d illustrates another side view of a stage in a horizontalprobing operation, according to another embodiment.

FIG. 7 a illustrates a side view of a stage motion profile, according toanother embodiment.

FIG. 7 b illustrates a side view of a stage acceleration profile,according to another embodiment.

FIG. 8 illustrates a side view of a possible embodiment of a probertesting system and its two main stages connected with a control system.

FIG. 9 illustrates a flow diagram showing exemplary operations of astage control process.

FIG. 10 illustrates a side view of a stage motion profile in comparisonto a parabolic motion profile.

FIG. 11 illustrates a side view of a possible embodiment of a probertesting system with added flexibilities between various components.

FIG. 12 illustrates an embodiment of acceleration sensing in a probertesting system with flexible connections.

FIG. 13 illustrates a block diagram of a feedback control schemeincorporating relative acceleration compensation.

FIG. 14 shows block diagram details of an acceleration compensationscheme based on relative acceleration measurements.

FIG. 15 shows the block diagram of the equivalent acceleration loop inFIG. 12 by adding acceleration based compensation.

FIG. 16 illustrates a flow diagram showing exemplary operations of atesting system that accurately maintains a desired probe-to-pad positionby incorporating motion disturbance sensing and compensation.

DETAILED DESCRIPTION

Various embodiments and aspects of the inventions will be described withreference to details discussed below, and the accompanying drawings willillustrate the various embodiments. The following description anddrawings are illustrative of the invention and are not to be construedas limiting the invention. Numerous specific details are described toprovide a through understanding of various embodiments of the presentinvention. However, in certain instances, well-known or conventionaldetails are not described in order to provide a concise discussion ofembodiments of the present inventions.

At least certain embodiments of the invention may be used to test orinspect a component such as an integrated circuit or a wafer containinga plurality of integrated circuits or a substrate containing one or moreother components. The following description is directed to waferprobing, but it will be understood that wafer probing is merely oneexample of an embodiment of the invention, and that all other examplesof other embodiments will not be used for wafer probing.

Wafer probing involves contacting the pad surface with probe tips. Probetips move or deform during the operation of probing. This action makesthe probe tips scrub or slide across the bond pads, balls/bumps orcontact surfaces of the wafer being tested. This mechanical action isnecessary to break through the contamination and oxide on the probe tipsand/or the pads. In addition, a large amount of pressure is used toscrub away an oxide or contamination layer.

In one embodiment of the present invention, a prober system consists oftwo main components, or stages, one holding a wafer and the other aprobe card. The two stages move relative to one another and are broughttogether in order to create the high pressure contact between the bondpads and the probe tips.

FIG. 2 shows a schematic of one such possible embodiment of a system100, comprising of two main stages. The main stages are the wafer holderassembly 102 and the probe-card holder assembly 104. In thisillustrative example, the wafer holder assembly 102 is capable of motionalong the X, Y, Z and θ_(g) directions while the probe card holderassembly (PCHA) 104 is held stationary. In another embodiment, the WHA102 can be held stationary while the PCHA 104 is capable of motion. Inyet another embodiment, the WHA 102 and PCHA 104 can both be capable ofmotion. In addition, the wafer 106 itself can be rotated around theθ_(w) direction relative to its holding chuck 108 in the wafer holderassembly 102. In this manner, the wafer 106 being supported by the waferholder assembly 102 can be moved relative to the probe card pins 158being supported by the probe-card holder assembly 104 so that the pins158 can be brought in contact with conductive elements 110 such as padsor balls/bumps on the wafer 106.

The wafer holder assembly 102 is supported by a granite base 112 and ametal frame 114 which is located on a support surface 116. The waferholder assembly 102 includes a motion system 118, a Z stage 120, and aholding chuck 108. The holding chuck 108, in one embodiment, holds thewafer 106 to present a number of bond pads 110 a for testing. The chuck108, being movable in the X,Y,Z and θ_(g) directions 122, is connectedto the Z-stage 120 of the gantry. The X-Y motion system 118, in oneembodiment, can be an X-Y gantry system which allows an X stage 138 tomove in the X-direction and a Y-stage 146 to move in a Y-direction. TheX-Y motion system 118 is connected with a Z stage 120 which is capableof moving in the Z-direction 154 to allow the probe pins 158 to makecontact with the pads 110 a on the wafer 106. The X-Y motion system 118is also connected with an encoder or sensors to track the position,velocity, and acceleration of the Z-stage 120 and wafer 106.

It is also appreciated, in another embodiment, that the Z stage 120floats above a granite base having a series of evenly distributed airorifices which blow air upwards towards the Z stage 120 in order to helpit move smoothly over the granite base 112 and thus alleviate some ofthe contact friction between the Z stage 120 and the granite base 112.

In another embodiment, the X-Y motion system 118 can also be a sawyermotor system having a smooth platen surface, a magnetized forcer, anddriving coils which affect the magnetic flux of the forcer to move the Zstage 120 in an X or Y direction 140,150 over the surface of the platen.In the sawyer motor system, the platen is a non-porous surface so thatair bearings mounted to the wafer holder assembly 102 can create apressurized region between the wafer holder assembly 102 and the platensurface. Air bearings, such as orifice air bearings or porous mediabearings, are attached to the lower surface of the Z-stage 120 to blowdownward toward the platen thus creating a uniform air gap between theZ-stage 120 and platen.

FIG. 2 further shows a probe card holder assembly 104 which includes asupport member or assembly 124, a ring carrier 126, a probe card 128,and probe tips 158. The ring carrier 126 is supported by the supportassembly 124 and can be made of a metal such as aluminum or steel. Thesupport assembly 124 is connected with the metal frame 114 which isconnected with the granite base 112. In this embodiment, the probe cardholder assembly 104 is stationary; however, it is possible to providethe probe card holder assembly 104 with a motion mechanism so that theprobe card can move with respect to the wafer holder assembly 102.

The probe card 128 is connected with the probe tips 158 and presents theprobe tips 158 for contact with the wafer 106. In this illustrativeexample, when the Z-stage 120 is actuated, the probe tips 158 come intocontact with the conductive elements 110.

The system 100 may be moved on wheels, such as wheels 130 and 132. Thewheels 130 and 132 are preferably part of a set of wheels, such as fourwheels, although any number of wheels can be used. The wheels can beretracted so that the metal frame 114 and granite base 112 rests on thefloor either directly on the floor or by retractable legs. In FIG. 2,the wheels 130 and 132 are in a retracted position although the wheelscan be moved into an extended position so that the system 100 can berolled across the support surface 116 making the system 100 portable.

FIG. 3 is a top view of the system 100 shown in FIG. 2. FIG. 3illustrates an example where the X-Y motion system 118 is an X-Y gantrysystem 134, as briefly mentioned above. In the X-Y gantry system 134, aset of two X rails 136 allows the Z-stage 120 to move in a linear andlow friction manner in the X-direction 140. The X rails 136 channel themotion of the Z-stage 120 so that a motion in the Y-direction is limitedor non-existent. A bridge 138 (or X-stage) rests on top of the granitebase 112 and X rails 136. The bridge 138 is connected with the Z-stage120 and it is possible to have the Z-stage 120 be independentlysupported by air bearings or blow holes. The bridge 138 also isconnected with the chuck 108 which holds the wafer 106 and itsconductive elements 110. The chuck 108 is moved along the X direction140 on the X rails 136 with respect to the granite base 112 by twoX-motors 142 that are connected with the bridge 138. It is appreciatedthat the chuck 108 can be moved in the X-direction 140 by one X-motor,or any number of motors, instead of only two motors. An additionalmotion mechanism housed in the gantry system can move the chuck 108 inthe Y, Z, and theta (θ) directions.

FIG. 3, according to one embodiment, shows an X-Y gantry system 134comprised of a Y-motor 144 connected with a Y-stage 146 that isconnected with two Y-rails 148 that guide the Y-stage 146 in aY-direction 150. The Z-stage 120 is supported or connected with theY-stage 146 so that the chuck 108 and wafer 106 (not shown in this view)can also be moved in the Y-direction 150. The Y-motor 144 could bemounted within the X-Y motion system 118 or it could be remotely mountedand connected with the Y-stage 146 to enable the chuck 108 to be movedin the Y-direction 150.

FIG. 3 also shows, according to one embodiment, a brushless rotary motor152 within the X-Y motion system 118 that is capable of raising theZ-stage 120 in a Z-direction 154 or theta (θ_(g)) 156 direction.Depending on the specific use of the system, the rotary motor 152 can bereplaced or used in combination with piezo-electric elevatingmechanisms, linear motors, ball and screw arrangements, slidermechanisms that transfer a lateral force to a vertical force to drivethe Z-stage 120 in the Z-direction 154, air bearings, or shape memoryalloy material for moving the Z-stage 120 in the Z-direction 154. Therotary motor 152 is preferably mounted within the X-Y motion system 118;however, in another embodiment, the rotary motor 152 can be remotelymounted to drive the Z-stage 120 in the Z-direction 154 or theta 156direction.

FIG. 4 shows a close-up side view of ring carrier 126, probe card 128and probe pins 158 in contact with bond pads 110 a so that the probepins 158 create an electrical contact with the bond pads 110 a. TheZ-stage 120, holding chuck 108, and component or wafer 106 are locatedin a contact position 164. A Z-stage 120 first contact position height162 is shown. A Z-stage 120 reference point 160 is located on a topportion of the Z-stage 120 and is directly aligned with the contactposition height 162 when the component or wafer 106 is in contact withthe probe pins 158. The Z-stage 120 reference point 160 is shown to belocated at the topmost portion of the Z-stage 120, below the holdingchuck 108 and wafer 106, and located along a central axis 170 of theZ-stage 120. It is appreciated that the Z-stage 120 reference point 160is chosen in this location for the purposes of illustration and it ispossible for another reference point location to be chosen in order todescribe the same Z-stage 120 motion profile to be further described.

The Z-stage 120 can arrive at the first contact position height 162 byan upward movement in an upward or third direction 166 (or secondvertical direction) of the Z-stage 120. After the probe pins 158 contactthe component or wafer 106, the Z-stage 120 disengages the wafer 106from the probe-card holder assembly 104 by moving in a downward or firstdirection 168 (or first vertical direction).

The two-dimensional coordinate system 172 shows the Z-direction 154parallel with the central axis 170 of the Z-stage 120 and first andthird directions 168, 166. The direction perpendicular to theZ-direction 154 can be either the X direction 140, Y-direction 150, or acombination of X and Y directions 140, 150.

FIG. 5 a shows a motion profile 194 traced by the Z-stage 120 referencepoint 160 as the Z-stage 120 moves through three distinct lines ofmotion. The Z-axis and X or Y-axis define a plane within which theZ-stage 120 motion is illustrated.

It is appreciated that the above Z-stage 120 motion could occur in athree-dimensional space, outside of the illustrated plane, but for easeof illustration the examples set forth occur in a two dimensionalcoordinate system.

The Z-axis extends in a positive Z-direction 154 while the axisperpendicular to the Z-axis extends in an X-direction 140, Y-direction150, or both X and Y directions 140,150. The Z-stage reference point 160begins at a first starting point 174. The first starting point 174represents the Z-stage 120 when it is in the contact position 164 asshown in FIG. 4. The Z-stage 120 moves from the first starting point 174toward a second point 176 by following a first motion profile 178 in thefirst direction 168. The first direction 168 can also be described as amotion in the negative Z-direction 154 or first vertical direction. Thesecond point 176 is located within a plane defining a first clearanceheight 180.

In one embodiment of the invention, a clearance height 180,202 is aheight at which movement in a direction perpendicular to the firstdirection 168 can safely be achieved without damage to any componentswithin the system 100.

At the first clearance height 180, the Z-stage 120 can be movedlaterally (with respect to the first direction) with zero risk ofdamaging the probe pins 158, conductive elements 110, wafer 106, holdingchuck 108, probe card 128, ring carrier 126, Z-stage 120, or anycomponent within the system 100.

After moving through the first clearance height 180, the Z-stage 120follows a second motion profile 188 while moving toward a settle checkpoint 186. The second motion profile 188 is a curved non-parabolicmotion during stage 120 movement in the lateral direction. The settlecheck point 186 is a location where the Z-stage 120 will be allowed tosettle in the second direction 192 to within a threshold value. In oneembodiment, the Z-stage 120 only has one settle check point 186 betweenmoving the stage 120 in the first vertical direction 168 (beyond thefirst clearance height 180) and moving the stage 120 to the secondcontact position 198.

The second motion profile 188 has two segments of motion. The firstsegment 182 occurs immediately after the Z-stage 120 passes through thefirst clearance height 180 at second point 176 and approaches a bottompoint 190. The second segment 184 occurs between the bottom point 190and the settle check point 186.

The bottom point 190 is the farthest distance in the first direction 168the Z-stage 120 will travel throughout the entire motion profile 194. Inthe entire motion profile 194, the bottom point 190 occurs at a locationthat is non-equidistant between the second point 176 and the settlecheck point 186 along the second direction 192 that is perpendicular tothe first direction 168.

During the first segment 182, the Z-stage 120 begins to move in a seconddirection 192 simultaneously with the first direction 168. The seconddirection 192 can be in a positive X-direction 140 or Y-direction 150with respect to the coordinate system shown. After passing the bottompoint 190, the Z stage begins to move along the second segment 184toward the settle check point 186. The settle check point 186 is locatedat a second clearance height 202. The second clearance height 202 can bethe same height as the first clearance height 180 or can be differentdepending on system factors such as wafer 106 planarity, probe pinsizes, materials, bond pads, or any other relevant variable within thesystem 100. In one embodiment, the second clearance height 202 can haveup to a 20 micron difference when compared with the first clearanceheight 180.

In FIGS. 5 a and 5 b, the second clearance height 202 is shown as beingthe exact same value as the first clearance height 180 for ease ofdiscussion.

During motion in the second segment 184, the Z-stage 120 moves in athird direction 166 simultaneously with the second direction 192. It isalso possible that the second segment 184 can consist of a movement inthe third direction 166 simultaneously with another direction other thanthe second direction 192 (being in a different plane). It should benoted that the first direction 168 is perpendicular to the seconddirection 192 and is parallel and opposite to the third direction 166.

After reaching the settle check point 186, the Z-stage 120 moves inpurely the third direction 166 along a third motion profile 196 toapproach a second contact position 198 located at a second contactposition height 200. The second contact position height 200 may be thesame height as the first contact position height 162 or it may be asubstantially different height depending on the previously mentionedsystem factors such as wafer 106 planarity, probe pin sizes, materials,bond pads, or any other relevant variable within the system 100. Again,the second contact position height 200 is shown as being the same heightas the first contact position height 162 for ease of discussion.

As mentioned, the Z-stage 120 will travel a distance along the thirdmotion profile 196. The distance traveled by the third motion profile196 is defined by the clearance gap distance 204 within which a Z-stage120 must be isolated from lateral movement. If lateral movement of theZ-stage 120 occurs while the Z-stage 120 is within the clearance gapdistance 204, the risk of damaging the system 100 components is present.

The clearance gap distance 204 defines the distance between theclearance heights 180,202 and the contact position heights 162, 200. Inone embodiment, the clearance gap distance 204 can be within the rangeof at least 125 microns (μ). In another embodiment, the clearance gapdistance 204 is within the range of 125μ-1 mm. Of course, the clearancedistance 204 could be up to several millimeters depending on system 100components and control parameters.

FIG. 5 a shows a die step size 254 which defines the distance betweenthe first and second contact positions 174, 198. The die step size 254has a midpoint which has a distance value of half the step size. TheZ-stage 120 reaches a bottom point 190 before reaching the midpointbetween the two contact positions 174, 198.

In one example, according to one embodiment, the Z-stage 120 travelsalong a first motion profile 178 through a distance of 0.330 mm. Theclearance gap distance 204 in this example is also 0.330 mm. During thesecond motion profile 188, the Z-stage 120 moves in the second direction192 a die step size 254 of 6.5 mm in-between the second point 176 andsettle check point 186. The Z-stage 120 then moves upward in the thirddirection 166 a distance of 0.330 mm to the second contact position 198along the third motion profile 196. Furthermore, in this example, thedistance in the first direction 168 (or negative Z-direction) betweenthe second point 176 and the bottom point 190 is about 0.15 mm-0.165 mmin a turn around period 224 later described. Therefore, the total traveldistance of the Z-stage 120 in the first direction is about 0.480-0.495mm.

According to the embodiment described, the travel distance of the firstmotion profile 178 in the first direction 168 and the third motionprofile 196 in the third direction 166 are both equal to the clearancedistance 204 to avoid damage to system 100 components.

According to another embodiment, it would be possible to have the firstmotion profile 178 and second motion profile 196 each greater in lengththan the gap distance 204; however, such a system would increase thetotal travel distance of the Z-stage 120 thereby decreasing theefficiency of the movement of the stage 120.

FIG. 5 b shows an acceleration profile 206 of the motion profile 194described in FIG. 5 a. The motion profile 194 of FIG. 5 a is generallyshown by a dotted line in FIG. 5 b for reference. The first accelerationprofile 208 is described with reference to first acceleration axis a1and first distance axis d1. According to this exemplary embodiment, thefirst acceleration axis a1 is perpendicular to the first direction 168and increases in a positive X-direction 140, Y-direction 150, or X and Ydirection. The first distance axis d1 is parallel with the firstdirection 168 and increases in a negative Z-direction 154.

The first acceleration profile 208 has two segments 210, 212 whichdescribe the acceleration behavior of the motion profile 194 in thefirst direction 168. The Z-stage 120 begins at zero acceleration atfirst starting point 174. As the Z-stage 120 moves in the firstdirection 168 it accelerates toward the second point 176 at anincreasing constant acceleration exemplified by acceleration segment210.

When the Z-stage 120 reaches the second point 176, the Z-stage isaccelerating at a peak acceleration 214 at the first clearance height180. In one embodiment, the acceleration and deceleration in the firstdirection 168 is approximately 0.7 g (0.3 g-1 g).

It is appreciated that the acceleration of the Z-stage 120 should be ashigh as possible being limited by system abilities. For example, changesin amplifiers, number of amps, power supply, size of the system, stageinertia, and other system 100 component parameters will affect theability of the Z-stage 120 to accelerate at specific rates. Theacceleration can be increased or decreased by changing certain system100 variables. For example, a smaller stage size with less inertiaduring movement may achieve faster indexing times and acceleration thansystems with a larger stage size.

Maintaining a maximum acceleration and deceleration value throughout thestage movement is critical in taking advantage of the efficient motionprofile 194 described.

After passing the second point 176, the Z-stage 120 begins to deceleratein the first direction 168 with respect to the acceleration axis a1 anddistance axis d1, as exemplified by the deceleration segment 212 (shownas a dotted line for clarity). The Z-stage 120 decelerates in the firstdirection 168 until it reaches bottom point 190 when movement in thefirst direction 68 is completed and acceleration in the first direction168 decreases to zero 216.

As the Z-stage 120 is decelerating in the first direction 168 afterpassing the first clearance height 180, a deceleration also occurs inthe second direction 192. The second acceleration profile 218 isdescribed with reference to second acceleration axis a2 and seconddistance axis d2. According to this exemplary embodiment, the secondacceleration axis a2 is perpendicular to the second direction 192 andparallel to the first direction 168. The second acceleration axis a2increases in a positive Z-direction 154. The second distance axis d2 isperpendicular with the first direction 168 and parallel with the seconddirection 192. The second distance axis d2 is increasing in a positiveX-direction 140, Y-direction 150, or both X and Y directions 140, 150.

FIG. 5 b further shows the second acceleration profile 218 having twosegments 220, 222 which describe the acceleration behavior of the motionprofile 194 in the second direction 192. The deceleration segment 220 isrelated directly to the first motion segment 182 (of the second motionprofile 188) previously described. On the same token, the accelerationsegment 222 is related directly to the second motion segment 184 shownin FIG. 5 a.

As the Z-stage 120 moves in the second direction 192 simultaneously withthe first direction 168, the Z-stage 120 decelerates from the secondpoint 176 to the bottom point 190 in both first and second directions168, 192. In one embodiment, the Z-stage 120 may experience anacceleration in the second direction 192 simultaneously with thedeceleration in the first direction 168. In one embodiment, theacceleration and deceleration value of the Z-stage 120 in the seconddirection 192 is approximately 0.7 g (0.3 g-1 g). As previouslydescribed, acceleration values can be affected by many system 100variables.

Because there is deceleration in the first 168 direction, this regioncan be referred to as a turn around period 224, being closely related tothe Z-stage 120 motion in the first segment 182 of the second motionprofile 188.

In the previously described example, the distance in the first direction168 (or negative Z-direction) between the second point 176 and thebottom point 190 was about 0.15 mm-0.165 mm in a turn around period 224and the Z-stage 120 traveled along a first motion profile 178 through adistance of 0.330 mm. The distance between the second point 176 and thebottom point 190 also represents the distance that the Z-stage 120travels in the first direction during the turn around period 224. Theturn around period 224 is where the lateral movement in the seconddirection 192 begins and Z-stage 120 deceleration begins to occurlaterally as well as vertically.

The Z-stage 120 accelerates through the first clearance height 180 andhas a deceleration distance 280 of about one-third of the total verticaltravel distance 284 of the Z-stage 120 in the first direction 168 (0.165mm/0.495 mm=0.33). The deceleration distance 280 in the first direction168 (below the clearance height 180) is at most one-half of anacceleration distance 282 that occurs above the clearance height 180. Inother words, the deceleration distance 280 is at most one-half of theacceleration distance 282 of the stage in the first direction 168.

In one embodiment, the deceleration distance 280 in the first direction168 is at most one-half of the clearance gap distance 204 (if clearancegap distance 204 and acceleration distance 282 are equal).

FIG. 5 b shows the deceleration segment 220 with respect to accelerationaxis a2 and distance axis d2. The deceleration segment 220 representsthe Z-stage 120 decelerating in the second direction 192 until itreaches the bottom point 190. At bottom point 190, the deceleration inthe first direction 168 reaches a zero value 216, according to thedeceleration segment 212. Simultaneously, at bottom point 190, thedeceleration in the second direction 192 also reaches a zero valueaccording to deceleration segment 220. Bottom point 190 also representsthe point at which acceleration or deceleration in the first directionis complete.

After bottom point 190, a Z-stage 120 acceleration begins to occur inthe second direction 192 as represented by acceleration segment 222. Inone embodiment, it is understood that it may be possible for the Z-stage120 to accelerate in the second direction 192 before reaching bottompoint 190. During the acceleration segment 222, there is also anacceleration (not shown) occurring in the third direction 166. Accordingto one embodiment, the acceleration 222 continues in the second 192 andthird 166 directions (or laterally and vertically) until the stagereaches settle check point 186.

At settle check point 186, the control system 250 (later described indetail) determines whether movement in the X and Y directions 140, 150have been reduced to a threshold value, such as zero. As previouslydescribed, any lateral movement (or movement perpendicular to the thirddirection 166) of the Z-stage 120 when it is past the second clearanceheight 202, within the clearance gap distance 204, could cause potentialdamage to the system 100. The settle check point 186 is a location wherethe control system 250 ensures no damage will result from unwantedlateral movement. The settle check time required to ensure zero orminimal lateral movement of the Z-stage 120 at settle check can be asfast as 20 msec or can take as long as a few seconds.

In one embodiment, the settle check time is minimal and does notsignificantly hinder the movement of the Z-stage 120 so thatacceleration in the second direction 192 can occur constantly toward thesettle check point 186, as exemplified by acceleration segment 222.

In another embodiment, the settle check time may be significant and thuscan require the Z-stage 120 to decelerate in all directions to astopping point in order to allow lateral movement to be isolated.

FIG. 5 b also shows a third acceleration profile 226, where the Z-stage120 accelerates to a midpoint 228 during acceleration segment 230. TheZ-stage 120 then decelerates, during deceleration segment 232, to thesecond contact position 198. In one embodiment, the acceleration anddeceleration in the third direction 166 is approximately 0.7 g (0.3 g-1g). Again, acceleration values are affected by many system 100variables.

FIGS. 6 a-6 d show the movement of the Z-stage 120 and its interactionwith the probe needles 158 during the entire motion profile 194described in FIGS. 5 a and 5 b except that the Z-stage 120 central axis170 is oriented in a horizontal direction for side probing. FIGS. 6 a-6d emphasizes side probing and the fact that the Z-stage 120 does notneed to be oriented in a vertical direction with respect to a supportsurface or base. The reference point 160 in FIGS. 6 a-6 d follows themotion profile 194 as mentioned.

FIG. 6 a shows the Z-stage 120 moving in the first direction 168 alongthe first motion profile 178. FIG. 6 b shows the Z-stage 120 movingalong the second motion profile 188, 182 in a first direction 168 andsecond direction 192, as generally indicated by an arrow 234. FIG. 6 cshows the Z-stage 120 moving in a third direction 166 and seconddirection 192 generally indicated by an arrow 236 after having passedthe bottom point 190. FIG. 6 d shows the Z-stage 120 moving in the thirddirection 166 to the second contact position 198 where the Z-stage 120allows the probe pins 158 to contact the bond pads 110 a in anotherlocation on the wafer 106.

FIG. 7 a shows another embodiment related to a motion profile 244 havingan alternative second motion profile 238. In this embodiment, the firstand third motion profiles 178, 196 are similar to those described inFIG. 5 a. However, there is an alternative second motion profile 238where the Z-stage 120 decelerates to an alternative bottom point 242 andthen accelerates to a check point 240. The check point 240 can be usedfor many different uses. For example, an inspection process can beimplemented at check point 240 or the control system 250 can checkwhether vertical motion is complete before proceeding. The check point240 can be a pause in the Z-stage 120 motion 244 or can be a relativelyfluid motion allowing the Z-stage 120 to constantly accelerate in thesecond direction 192 to reach the settle check point 186.

After the check point 240, the Z-stage 120 then moves in the seconddirection 192 toward the settle check point 186. The second motionprofile 188 of FIG. 5 a is shown in a dotted line for discussion andreference. The alternative bottom point 242 occurs slightly earlier inthe second direction than the bottom point 190 of motion profile 188.

FIG. 7 b illustrates the acceleration profile of the motion profile 244shown in FIG. 7 a. During the alternative second motion profile 238, theZ-stage 120 accelerates from the bottom point 242 to the check point240. The Z-stage 120 can continue to accelerate after the check point240 in the second direction 192. The Z-stage 120 acceleration in thesecond direction 192 is then described by reference to acceleration axisa3 and distance axis d3. The Z-stage 120 continues to accelerateprimarily in the second direction until a midpoint 246 at which theZ-stage 120 begins to decelerate to arrive at the settle check point186. Again, the check point 240 can also be a location where the Z-stage120 pauses for a time period before proceeding, in which case adeceleration in the second direction 192 would be required.

FIG. 8 shows the system 100 and its connections with a sensor 248 andcontrol system 250. Specifically, a sensor 248 is in communication withor connected with motion system 118 and Z-stage 120 so that a parameterof the Z-stage 120 is accurately known at all times. The parametermeasured by the sensor 248 can be a position, velocity, or accelerationof the Z-stage 120. The sensor 248 relays information to the controlsystem 250 so that precise motion control commands can be communicatedto the mechanisms that move the Z-stage 120, such as motors 142, 144.The sensor 248 can be any type of sensor such as an encoder, camerasystem, or any known motion control sensor.

In one embodiment, the control system 250 is a model based controlsystem that can predict motion profiles, trajectories, and settle timesas further described in detail.

FIG. 9 illustrates a flow chart describing a control process 252 of thecontrol system 250. The control process 252 begins by determining 256 orreading the clearance distance 204 and die step size 254. The clearancedistance 204 and die step size 254 can be input parameters (inputautomatically by a system or manually by a user) being dependent onvarious parameters of the system 100, such as what type of wafer 106,component, or probe pins 158 are being used. Also, a starting locationon the wafer 106 should be determined for the probe pins 158 to makecontact with the wafer 106. From the clearance distance 204, a firstclearance height 180 and second clearance height 202 can be calculatedfor the Z-stage 120.

The control process 252 also determines 258 the Z-movement distance foraccelerating in the negative Z-direction 154 (such as first direction168). The control process 252 proceeds to accelerate 260 the stage inthe negative Z-direction 154 past a clearance height.

Upon passing the clearance height, the Z-stage 120 begins to coast 262in the negative Z-direction 154 causing a deceleration whilesimultaneously beginning a motion in the X-direction 140, Y-direction150, or both X and Y directions 140, 150. The coasting 262 effect can beaccomplished by adjusting a motor parameter, such as current, to causethe motor to decelerate. By applying a current in the oppositedirection, the motors can decelerate as quickly as they accelerated.Coasting can also be achieved by shutting off the Z-direction 154 motoruntil the Z-stage 120 decelerates to zero at a bottom point.

FIG. 9 further shows a step and repeat process. The Z-stage 120accelerates 264 in a positive Z-direction 154 after reaching a bottompoint. The control process 252 constantly monitors 266 whether theZ-stage 120 has reached the second clearance height 202 or a settlecheck point. If the second clearance height 202 is not reached, theZ-stage 120 continues to accelerate in the positive Z-direction 154. Ifthe second clearance height 202 is reached, the control process 252checks 268 whether there is movement in the X-direction 140 orY-direction 150 and whether that movement is below a threshold value.

In one embodiment, the control process checks 268 whether X or Ymovement is done by monitoring the sensor 248. The sensor 248, which canbe a plurality of sensors or just one sensor, is connected with ormonitors the motion system 118 which can be an X-Y gantry system 134shown in FIG. 3.

According to one embodiment, in the X-Y gantry system 134, the sensor248 monitors whether the movement in the X-stage 138 and/or Y-stage 146has stopped or dropped below a threshold value (safety check). If nomovement is detected in the X and Y stages 138, 146 but the secondclearance height 202 has not been reached yet, then the Z-stage 120 willcontinue to accelerate in the Z-direction 154 until the second clearanceheight 202 is reached.

In FIG. 9, if the Z-stage 120 is located at the second clearance height202 but motion in the X and/or Y directions 140,150 is still present inthe system 100, the Z-stage 120 will stop moving 270 in the positiveZ-direction 154 to prevent X-Y motion from occurring above the secondclearance height 202. The control process 252 continues to check 272whether the motion in the X and/or Y directions is present. If the X-Ymotion continues, the Z-stage 120 will be maintained at the clearanceheight until such X-Y motion is finished. After the X-Y motion isfinished and the Z-stage 120 is located at the second clearance height202, the Z-stage 120 will finish moving 274 in positive Z-direction 154to a commanded touchdown position where testing will begin on the wafer106.

According to another embodiment, trajectory calculations are made atevery motion profile or movement, to minimize motion times by optimizingacceleration times and distances, while maintaining wafer 106 and probecard 126 safety. This update to the motion profile happens every 50microseconds.

By incorporating a high update rate, safety checks can occur inconjunction with a stage movement rather than after the completion ofthe move. By using a model based control, the settle time (t*—the timeat which the X-Y motion will have settled to within a specifiedtolerance) can be predicted. The Z-component of the trajectory canthereby be planned (timed) so that the wafer doesn't come into contactwith the probe pins 158 until after the X-Y motion has sufficientlysettled. Conversely, the X-Y trajectory for the die-step can be planned(timed) to start when the Z-trajectory or motion profile displaces thewafer safely out of contact with the probe pins. Thus, the presentinvention speeds the time to step from one die to the next butaccomplishes this with a deterministic lift-off and touchdowntrajectory.

FIG. 10 shows the non-parabolic motion profile 194 of FIG. 5 a incomparison with a parabolic shaped motion profile 276 with midpoint 278.The present invention has significant advantages over a parabolic shapedmotion profile 276. The parabolic shaped motion profile 276 showslateral movement before reaching a clearance height and has asubstantial risk of damaging components. Furthermore, the parabolicshaped motion profile 276 may be shorter in travel distance than motionprofile 276, but the parabolic motion profile 276 will move slower thanthe motion profile 194. Thus, the parabolic profile 276 will have alonger “index time”. Even though the motion profile 194 travels a longerdistance than parabolic profile 276, the present invention spends moretime accelerating than decelerating. The motion profile 194 beginsacceleration in the second direction 192 at bottom point 190 whereas theparabolic profile 276 begins acceleration at a later midpoint 278. As aresult, the motion profile 194 is more effective and efficient by havinga shorter index time and longer acceleration times.

The acceleration of the Z-stage 120 in a the first vertical direction168 through the first clearance height 180 occurs during a first timeperiod greater than a second time period when the Z-stage 120 isdecelerating after passing through the clearance height 180.

The present invention has an important advantage over the prior artshown FIGS. 1 a and 1 b in that the “index time” for a Z-stage 120 tomove from one contact position to another contact position is greatlyreduced. In the scenario where the Z-stage 120 moves 6.5 mm (step size254) in the second direction between two contact positions, the presentinvention would complete the entire movement in 230-242 msec. Incontrast, the prior art described in FIGS. 1 a and 1 b would completethe movement in about 319 msec. The present invention achieves adecrease in index time between contact positions of about 24-30% overthe prior art.

In one embodiment, the settling time of the present invention can be asfast as 20 msec whereas the settling time of the prior art will take atleast as long as 40 msec or greater. The present invention significantlyreduces settling time for a stage.

In one embodiment, the settling time can be planned or predicted bymodel based control as previously described. Empirical data can be usedto predict a settle time or motion trajectory based on factors such asprior stage movements, the type of components being tested, amplifiers,number of amps, power supply, size of the system, stage inertia, andother system component parameters

Moreover, the acceleration profile described in the present inventionachieves a Z-motion having about two-thirds acceleration and one-thirddeceleration in the Z-direction 154. The known prior art has a Z-motionhaving only one-half acceleration and one-half deceleration in theZ-direction 154. The present invention may move farther in theZ-direction 154 than the prior art but spends less time moving in theZ-direction 154.

Another advantage of the present invention is that deceleration time inthe Z-direction is decreased and acceleration time in the Z-direction isincreased by accelerating the stage full speed past the minimumclearance distance. Deceleration occurs in the lateral movement whichreduces indexing time. The present invention reduces waiting time andtherefore increases efficiency and production abilities.

The stage control process 252 and methods described can be implementedin “direct write” operations such as ink jet, nozzle dispensingprocesses, aerosol spray coating, soft lithography, laser guidanceapproaches, AFM dip-pen techniques, or any technique or process capableof depositing, dispensing, or processing different types of materialsover various surfaces following a preset pattern or layout. The controlprocess 252 can quickly and efficiently move a stage holding amanufacturing component within the described processes. The controlprocess 252 can be applied to fabrication systems for electronicdevices, sensors, MEMS devices, and other known devices.

The control process 252 and methods described can be used with systemshandling a broad range of materials such as all types of glass andmetal, alloys, semiconductors, crystals, synthetic materials, ceramics,plastics, and natural organic materials including biological material.

The control process 252 and methods described can be used in aninspection stage system instead of a wafer probing system. In aninspection stage system, the contact positions 174, 198 would beconsidered inspection positions where a wafer, electronic device, orcomponent is examined or imaged for defects. The stage 120 movement inthe inspection stage system would apply the same methods and principlesalready discussed.

In a typical system the connections joining the different components arelikely to exhibit flexibilities. Because the connections betweencomponents are not perfectly rigid there will be vibrationary orflexural relative displacements between the components of the systemwhen a part of the system is exposed to a disturbance. The flexuraldeflections may in turn cause non-compensatory dislocations between thewafer pad and the probe card pins, thus degrading performance.

FIG. 11 depicts a possible embodiment of a probing system 300 presentingflexural connections between some of the various components. A number ofexemplary non-rigid connections between some of the components are shownin FIG. 11. Thus, the joint 310 between the Z stage 302 and the granitebase 301 is illustrated with a spring symbol 310 to indicate theflexural (and vibratory) nature of the joint. The actuation system 308is connected to the gantry system. Similarly, the connection 309 betweenthe Probe-card Holder Assembly (PHA) stage 315, 316 and the granite base301 of the Wafer Holder Assembly (WHA) stage 314 as well as the joint311 between the granite base 301 and the floor 312 are also illustratedwith spring symbols. It will be understood that actual physical springsare not present but that the joints may be modeled or represented bythese springs. The coordinate system 313 is illustrated for clarity. Aprobe card holder chuck 306 maintains a probe card 307 against the bondpads 305 on a wafer 304.

Unwanted relative displacements can be reduced by increasing theflexural rigidity of the connections, or by providing isolation betweenthe floor and the system. These methods have the disadvantage ofrequiring an increase in the weight of the system (thereby raising thesensitivity in the frequency domain to motion disturbances), and ofrequiring a change in the isolation properties at installation of aprobing system. A less costly and complex solution that would reduce theeffect of unwanted vibrations is to actively suppress or compensate forthe motion disturbances via a sensing and control system.

In a possible embodiment of another aspect of the invention, disturbancemeasurement devices can be added to several locations on the probingsystem. For example, one sensor could be placed on the granite base,another on the XYZ motion mechanism on the gantry system and a third onthe probe pin locating interface. Disturbance amplitude and phaseinformation is measured continuously at all three locations and alongdifferent directions (X, Y and Z). The sensing information could beinput into the motion controller through low pass filters to eliminatehigh-frequency noise in the signals. The controller would then processthe relative amplitude and phase information to apply compensatorycorrections to the system in the X,Y,Z or theta directions through themotion mechanism's existing actuation drives. The resultant motion isdevoid of all uncontrolled relative displacements between the wafersubstrate and the probe pins. In addition, the corrections would allowthe system to step from die to die on the wafer much faster because theaccelerometers would also be used to cancel out the reaction forces(internal disturbances) as the wafer chuck moves from probing one die toa position to probe the next die.

FIG. 12 shows the same side view of the exemplary probing systempresented in FIG. 11 with the addition of accelerometers at threedifferent locations on the system. The boxes A₁ 412, A₂ 413 and A₃ 414represent three accelerometers added to measure the motion of thegranite base 301, the bridge/chuck/wafer assembly 402 (which can beassumed to be rigidly connected and thus considered as a singlevibratory element) and the PCHA stage 315, respectively. The coordinatesystem 407 is shown for clarity.

The addition of these three sensors allows quantification of themagnitude and phase of the vibratory accelerations and/or velocitiesinduced at each of these three locations by an external or internaldisturbance. Similarly, the measurements can be used to derive therelative acceleration, velocity, magnitude and phase between themeasured components. Both types of measurement, individual and relative,can be used in different control schemes to compensate for unwanteddisplacements.

It would be possible in another embodiment of the same aspect of theinvention to alternatively use velocity sensors or a combination ofvelocity and acceleration sensors or different numbers of sensors and atdifferent locations. It will also be appreciated that such sensors maybe used to compensate for motion disturbances in wafer probing systemswhich use sawyer motors (rather than a gantry system) to move one orboth of the wafer chuck and the probe card platform relative to eachother.

FIG. 13 shows a block diagram of a possible embodiment of a controlsystem incorporating acceleration information from two sensors 501 and502 located at the granite base and the gantry, respectively. Thisparticular embodiment serves to illustrate another aspect of theinvention, namely a control scheme designed to eliminate contactposition disturbances during operation. In the particular illustrativeembodiment shown in FIG. 13, the controller consists of two main loops:a position control loop 513 with its own position controller 508 and anacceleration control loop 514 with its own vibration controller 509.

As explained above, the Z stage is attached to the bridge of the gantrysystem and is floating on the granite base. The gantry is here assumedto comprise the bridge/chuck/wafer assembly 402 of FIG. 12. When theactuation motors drive the gantry forward, the same amount of tractionforce will act on the granite base with reverse direction (by Newton'sthird law of motion). This can be considered an internal disturbance.Similarly, any external disturbance acting on the base (for example fromfloor shaking) will also appear in the gantry because of the tractionforce between the gantry and the granite base. Because of the non-rigidconnection between the gantry and base, vibratory relative displacementswill be induced by such disturbances.

The design objective of the compensation scheme shown in FIG. 13 is toensure that both the gantry and the granite base have the same amplitudeand phase, that is, the control system is compensating for (oreliminating) the relative vibrations between the gantry and base.

For the purposes of this particular illustrative embodiment of thisaspect of the invention, it will be assumed that the there is a rigidconnection between the granite base and floor, and both will be viewedas a single spring-mass system with a mass M_(EQ) and a stiffnessK_(EQ). The stiffness K_(EQ) would correspond to the spring 310 shown inFIG. 12 between the base and gantry.

The floor/base structure can move relative to the mass of the gantry,which for this illustrative example will be assumed to be a linearsystem with mass M_(Gantry) and no stiffness of its own. Based on theabove assumptions, the dynamics of the gantry relative to the granitebase, termed G_(Gantry-on-Granite) (which will produce the relativemotion between the base and gantry that the controller in FIG. 13 isdesigned to suppress), can be written in the frequency domain as thefollowing transfer function:

$\begin{matrix}\begin{matrix}{{G_{{Gantry}\text{-}{on}\text{-}{Granite}}(s)} = \frac{{Acc}_{Relative}(s)}{F_{Actual}(s)}} \\{= {{G_{Gantry}(s)} + {G_{Granite}(s)}}} \\{= {\frac{1}{M_{Gantry}}\left( \frac{\frac{s^{2}}{\omega_{2}^{2}} + 1}{\frac{s^{2}}{\omega_{1}^{2}} + 1} \right)}}\end{matrix} & (1)\end{matrix}$where:

Acc_(Relative)(s) is the relative acceleration 503 between the base andgantry obtained by subtracting the accelerometer readings of the base511 and gantry 512.

F_(Actual)(s) is the control force 504 applied to the base and gantryresulting from the combined action of the Compensation force 510 and theDesired Control force 505.

G_(Gantry)(s) is the transfer function of the dynamics of the gantry.

G_(Granite)(s) is the transfer function of the dynamics of thefloor/base.

ω₁=√{square root over (K_(EQ)/M_(EQ))} is the resonant frequency of thefloor/base structure.

and ω₂=√{square root over (K_(EQ)/(M_(EQ) 30 M_(Gantry)))} is theresonant frequency of the gantry and floor/base masses combined.

Given the resonance (or poles, obtained by calculating the roots of thedenominator) of Eq. (1), which will be a combination of ω₁ and ω₂, itwould be difficult for a servo controller (which in FIG. 13 is acombination of a Position Controller 508 and a Vibration Controller 509)to obtain perfect tracking (i.e. zero position error 507) of a commandedposition 506. Therefore, it would be desirable to design a compensation510 that will also linearize the dynamics between the Desired Control505 and Relative Acceleration 503 signals in FIG. 13. In that case, theservo controller would have an ideal (zero) error control. In anotheraspect of the invention, an embodiment of the control scheme wouldinvolve such linearization.

FIG. 14 shows the block diagram of a possible embodiment of acompensation control 601, termed H_(Compensation) (and equivalent to theVibration Controller 509 in FIG. 13), designed to linearize the relativedynamics 604 between the base 602 and gantry 603 and thus eliminate theresonance. The resulting Compensation 605, or F_(Compensation), can bedesigned as follows:F _(Compensation) =M _(Gantry) ×Acc _(Granite)  (2)where Acc_(Granite) is the acceleration of the granite base.

Equation (2) is insensitive to the resonance frequency, as desired.Incorporating the relative dynamics of the gantry and base,G_(Gantry-on-Granite), into Equation (2) the compensation control,H_(Compensation) 601 can then derived as follows:

$\begin{matrix}\begin{matrix}{{H_{Compensation}(s)} = \frac{F_{Compensation}(s)}{{Acc}_{Relative}(s)}} \\{= {M_{Gantry} \cdot \frac{G_{Granite}(s)}{G_{{Gantry}\text{-}{on}\text{-}{Granite}}(s)}}}\end{matrix} & (3)\end{matrix}$

The equivalent system dynamics with the above compensation, termed^G_(Gantry-on-Granite), is then:

$\begin{matrix}{{{\hat{G}}_{{Gantry}\text{-}{on}\text{-}{Granite}}(s)} = \frac{G_{{Gantry}\text{-}{on}\text{-}{Granite}}(s)}{1 + {{G_{{Gantry}\text{-}{on}\text{-}{Granite}}(s)}{H_{Compensation}(s)}}}} & (4)\end{matrix}$Hence, the resultant system dynamics with compensation (substitutingEquations (2) and (3) into Equation (4)) will be:

$\begin{matrix}{{{\hat{G}}_{{Gantry}\text{-}{on}\text{-}{Granite}}(s)} = \frac{1}{M_{Gantry}}} & (5)\end{matrix}$

Comparing the relative dynamics with compensation ^G_(Gantry-on-Granite)in Equation (5) and the dynamics without compensationG_(Gantry-on-Granite) in Equation (1), it is clear that the resonancecaused by traction forces and external disturbances will be eliminatedwith the above compensation H_(Compensation). In practice,H_(Compensation) is expected to lead to an ideal linear system and thusto improved position tracking even when disturbances are present andcontinuous and during operation while the probe pins are contacting thebonding pads.

FIG. 15 shows the complete control block diagram when the accelerationbased compensation control 601 of FIG. 14 is incorporated 701 into theentire control scheme of FIG. 13.

Other embodiments of control systems incorporating the readings ofmultiple sensors of same or other kinds in order to achieve the accurateand continuous positioning of wafer pads relative to probe pins in anydirection and in the presence of motion disturbances are also covered bythe present invention. Similarly, other control schemes compensating forindividual (non-relative) or relative accelerations of differentcomponents in the system in different ways that result in activesuppression of motion disturbances in a probing system are also coveredby the present invention.

FIG. 16 is a flow diagram showing a possible embodiment of the processesinvolved in a testing system making use of sensors and a control systemto compensate for motion disturbances on the WHA stage. As a firstoperation 801, the WHA and PCHA stages are brought in contact until thedesired contact position and force is achieved. In order to maintainthat desired contact position, any vibration (magnitude and phase)between the gantry and base are continuously measured 802 to detectchanges in the desired contact position due to motion disturbances suchas floor shaking or actuation of the gantry. A control system thendetermines the required corrective action based on the sensorinformation 803. The corrective forces are then applied to the gantryvia actuators incorporated in the WHA stage to eliminate any unwantedposition disturbances and to track the desired position 804. Operations802-804 are continually repeated (for example every 50 milliseconds), inat least certain embodiments, to ensure that any disturbances to thedesired position are promptly corrected. These operations (802-804) arealso performed repeatedly (e.g. every 50 milliseconds) as the WHA andthe PCHA stages are moved relative to one another in order to step fromdie to die to position the probe tips over a new set of bonding pads inthe probing process. Other embodiments where other parameters andcomponents of the system are monitored and controlled are also possible.

The methods described herein can be performed by a data processingsystem, such as a general or special purpose computer, operating undersoftware control where the software can be stored in a variety ofcomputer readable media.

The various embodiments of the inventions may be used on wafer probershaving wafer chucks which hold full wafers or other types of probingsystems such as systems which probe die or dice on film frames (whichare flexible) or strips (which may be rigid).

Thus, apparatuses and methods have been provided for achieving andmaintaining the accurate pad to probe contact positioning in a testingsystem in the presence of disturbances. Although the present inventionhas been described with reference to specific exemplary embodiments, itwill be evident that various modifications and changes may be made tothese embodiments without departing from the broader spirit and scope ofthe invention as set forth in the claims. Accordingly the specificationand drawings are to be regarded in an illustrative rather than arestrictive manner.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will be evidentthat various modifications may be made thereto without departing fromthe broader spirit and scope of the invention as set forth in thefollowing claims. The specification and drawings are, accordingly, to beregarded in an illustrative sense rather than a restrictive sense.

1. A method of moving a wafer stage comprising: moving a wafer stage ofa probing system in a first direction through a clearance height,wherein moving the wafer stage through the clearance height changes adistance between the wafer stage and a probe tip of the probing system;moving, only after moving the wafer stage through the clearance height,the wafer stage to a bottom point in the first direction while movingthe wafer stage in a second direction, wherein the second direction isperpendicular to the first direction; and moving, after moving the waferstage to the bottom point, the wafer stage in a third direction, whereinthe third direction is parallel and opposite to the first direction. 2.The method of claim 1, wherein the wafer stage pauses after moving inthe third direction, before moving in the second direction to a settlecheck point.
 3. The method of claim 1, wherein moving the wafer stage inthe third direction occurs simultaneously with moving the wafer stage inthe second direction to a settle check point.
 4. The method of claim 1,further comprising allowing the wafer stage to settle at a settle checkpoint before moving the wafer stage in the third direction to a contactposition.
 5. The method of claim 1, wherein the wafer stage reaches thebottom point before moving through a midpoint between two contactpositions.
 6. The method of claim 4, wherein the wafer stage only hasone settle check point between moving the wafer stage through theclearance height to the contact position.
 7. The method of claim 4,wherein the wafer stage has a motion profile with a check point and thesettle check point between moving the wafer stage through the clearanceheight to the contact position.
 8. The method of claim 4, wherein thewafer stage moves in a curved non-parabolic motion while the wafer stagemoves in the second direction to arrive at the settle check point.
 9. Amachine readable medium having stored thereon data representingsequences of instructions, which when executed by a computer systemcause the computer system to perform a method comprising: moving a waferstage of a probing system in a first direction through a clearanceheight, wherein moving the wafer stage through the clearance heightchanges a distance between the wafer stage and a probe tip of theprobing system; moving, only after moving the wafer stage through theclearance height, the wafer stage to a bottom point in the firstdirection while moving the wafer stage in a second direction, whereinthe second direction is perpendicular to the first direction; andmoving, after moving the wafer stage to the bottom point, the waferstage in a third direction, wherein the third direction is parallel andopposite to the first direction.
 10. A wafer probing apparatuscomprising: a support frame; a base supported by the support frame; awafer stage supported by the base, the wafer stage being configured tomove in a three-dimensional coordinate system having three axes ofmotion; at least one motor connected with the wafer stage for moving thewafer stage in the three-dimensional coordinate system, the at least onemotor being configured to move the wafer stage in a first axis of motionthrough a clearance height to a bottom point while simultaneously movingthe wafer stage in a second axis of motion to the bottom point; and atleast one sensor coupled with the wafer stage, the sensor beingconfigured to measure a wafer stage position.
 11. The apparatus of claim10, wherein the at least one motor is a brushless motor.
 12. Theapparatus of claim 10, wherein the at least one motor is a sawyer motor.13. A method of moving a wafer stage comprising: accelerating a waferstage of a probing system in a first direction before moving the waferstage through a clearance height, wherein moving the wafer stage throughthe clearance height changes a distance between the wafer stage and aprobe tip of the probing system; accelerating the wafer stage in asecond direction while moving the wafer stage in the first direction;and accelerating the wafer stage in a third direction, wherein the firstdirection is perpendicular to the second direction and is parallel andopposite to the third direction.
 14. The method of claim 13, whereinaccelerating the wafer stage in the first direction occurs over anacceleration distance of about two-thirds of a total travel distance ofthe wafer stage in the first direction.
 15. The method of claim 13,further comprising decelerating the wafer stage in the first directionafter accelerating the wafer stage in the first direction, whereindecelerating the wafer stage in the first direction occurs over adeceleration distance of about one-third of a total travel distance ofthe wafer stage in the first direction.
 16. The method of claim 13,further comprising decelerating the wafer stage in the first directionafter accelerating the wafer stage in the first direction, whereindecelerating the wafer stage in the first direction occurs over adeceleration distance that is at most one-half of an accelerationdistance of the wafer stage in the first direction.
 17. The method ofclaim 13, wherein the clearance height is a distance from a contactposition, wherein after moving the wafer stage through the clearanceheight the wafer stage can move in the second direction without causingcontact with the probe tip.
 18. The method of claim 17, wherein theprobe tip is disposed on a probing system component selected from thegroup consisting of a probe card and a probe pin.
 19. The method ofclaim 17, wherein the clearance height is at least 125 microns from thecontact position.
 20. The method of claim 13, further comprisingdetermining whether movement of the wafer stage in the second directionis below a threshold value before continuing to move the wafer stagefurther in the third direction.
 21. The method of claim 13, whereinaccelerating the wafer stage in the first direction occurs at a maximumpossible acceleration rate.
 22. The method of claim 13, wherein movingthe wafer stage in the first direction while accelerating the waferstage in the second direction is achieved by adjusting a parameter of atleast one motor and coasting the wafer stage in the first direction. 23.A method of moving a wafer stage comprising: accelerating a wafer stageof a probing system in a vertical direction over a first time periodbefore moving the wafer stage through a clearance height, wherein movingthe wafer stage through the clearance height changes a distance betweenthe wafer stage and a probe tip of the probing system; decelerating thewafer stage in the vertical direction during a second time period,wherein the first time period is greater than the second time period;and accelerating the wafer stage in a horizontal direction whiledecelerating the wafer stage in the vertical direction.
 24. A machinereadable medium having stored thereon data representing sequences ofinstructions, which when executed by a computer system cause thecomputer system to perform a method comprising: accelerating a waferstage of a probing system in a first direction before moving the waferstage through a clearance height; wherein moving the wafer stage throughthe clearance height changes a distance between the wafer stage and aprobe tip of the probing system; accelerating the wafer stage in asecond direction while moving the wafer stage in the first direction;and accelerating the wafer stage in a third direction, wherein the firstdirection is perpendicular to the second direction and is parallel andopposite to the third direction.
 25. A probing system comprising: abase; a wafer stage supported by the base, the wafer stage beingconfigured to move in a three-dimensional coordinate system; at leastone motor connected with the wafer stage for moving the wafer stage inthe three-dimensional coordinate system, the at least one motor beingconfigured to accelerate the wafer stage in a first direction beforemoving the wafer stage through a clearance height and the at least onemotor being configured to accelerate the wafer stage in a seconddirection while moving the wafer stage in the first direction, whereinmoving the wafer stage through the clearance height changes a distancebetween the wafer stage and a probe tip of the probing system; at leastone sensor coupled with the wafer stage, the sensor being configured tomeasure a wafer stage parameter; and a control system being configuredto receive information from the at least one sensor and determineoperating parameters of the at least one motor based on a clearanceheight parameter.